diff options
| -rw-r--r-- | Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt | 34 | ||||
| -rw-r--r-- | drivers/video/backlight/adp8860_bl.c | 1 | ||||
| -rw-r--r-- | drivers/video/backlight/pwm_bl.c | 232 | ||||
| -rw-r--r-- | include/linux/backlight.h | 1 |
4 files changed, 247 insertions, 21 deletions
diff --git a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt index 310810906613..64fa2fbd98c9 100644 --- a/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt +++ b/Documentation/devicetree/bindings/leds/backlight/pwm-backlight.txt @@ -3,13 +3,6 @@ pwm-backlight bindings Required properties: - compatible: "pwm-backlight" - pwms: OF device-tree PWM specification (see PWM binding[0]) - - brightness-levels: Array of distinct brightness levels. Typically these - are in the range from 0 to 255, but any range starting at 0 will do. - The actual brightness level (PWM duty cycle) will be interpolated - from these values. 0 means a 0% duty cycle (darkest/off), while the - last value in the array represents a 100% duty cycle (brightest). - - default-brightness-level: the default brightness level (index into the - array defined by the "brightness-levels" property) - power-supply: regulator for supply voltage Optional properties: @@ -21,6 +14,19 @@ Optional properties: and enabling the backlight using GPIO. - pwm-off-delay-ms: Delay in ms between disabling the backlight using GPIO and setting PWM value to 0. + - brightness-levels: Array of distinct brightness levels. Typically these + are in the range from 0 to 255, but any range starting at + 0 will do. The actual brightness level (PWM duty cycle) + will be interpolated from these values. 0 means a 0% duty + cycle (darkest/off), while the last value in the array + represents a 100% duty cycle (brightest). + - default-brightness-level: The default brightness level (index into the + array defined by the "brightness-levels" property). + - num-interpolated-steps: Number of interpolated steps between each value + of brightness-levels table. This way a high + resolution pwm duty cycle can be used without + having to list out every possible value in the + brightness-level array. [0]: Documentation/devicetree/bindings/pwm/pwm.txt [1]: Documentation/devicetree/bindings/gpio/gpio.txt @@ -39,3 +45,17 @@ Example: post-pwm-on-delay-ms = <10>; pwm-off-delay-ms = <10>; }; + +Example using num-interpolation-steps: + + backlight { + compatible = "pwm-backlight"; + pwms = <&pwm 0 5000000>; + + brightness-levels = <0 2048 4096 8192 16384 65535>; + num-interpolated-steps = <2048>; + default-brightness-level = <4096>; + + power-supply = <&vdd_bl_reg>; + enable-gpios = <&gpio 58 0>; + }; diff --git a/drivers/video/backlight/adp8860_bl.c b/drivers/video/backlight/adp8860_bl.c index 16119bde9750..f1dc41cf19e3 100644 --- a/drivers/video/backlight/adp8860_bl.c +++ b/drivers/video/backlight/adp8860_bl.c @@ -690,6 +690,7 @@ static int adp8860_probe(struct i2c_client *client, switch (ADP8860_MANID(reg_val)) { case ADP8863_MANUFID: data->gdwn_dis = !!pdata->gdwn_dis; + /* fall through */ case ADP8860_MANUFID: data->en_ambl_sens = !!pdata->en_ambl_sens; break; diff --git a/drivers/video/backlight/pwm_bl.c b/drivers/video/backlight/pwm_bl.c index 44ac5bde4e9d..bdfcc0a71db1 100644 --- a/drivers/video/backlight/pwm_bl.c +++ b/drivers/video/backlight/pwm_bl.c @@ -143,11 +143,116 @@ static const struct backlight_ops pwm_backlight_ops = { }; #ifdef CONFIG_OF +#define PWM_LUMINANCE_SCALE 10000 /* luminance scale */ + +/* An integer based power function */ +static u64 int_pow(u64 base, int exp) +{ + u64 result = 1; + + while (exp) { + if (exp & 1) + result *= base; + exp >>= 1; + base *= base; + } + + return result; +} + +/* + * CIE lightness to PWM conversion. + * + * The CIE 1931 lightness formula is what actually describes how we perceive + * light: + * Y = (L* / 902.3) if L* ≤ 0.08856 + * Y = ((L* + 16) / 116)^3 if L* > 0.08856 + * + * Where Y is the luminance, the amount of light coming out of the screen, and + * is a number between 0.0 and 1.0; and L* is the lightness, how bright a human + * perceives the screen to be, and is a number between 0 and 100. + * + * The following function does the fixed point maths needed to implement the + * above formula. + */ +static u64 cie1931(unsigned int lightness, unsigned int scale) +{ + u64 retval; + + lightness *= 100; + if (lightness <= (8 * scale)) { + retval = DIV_ROUND_CLOSEST_ULL(lightness * 10, 9023); + } else { + retval = int_pow((lightness + (16 * scale)) / 116, 3); + retval = DIV_ROUND_CLOSEST_ULL(retval, (scale * scale)); + } + + return retval; +} + +/* + * Create a default correction table for PWM values to create linear brightness + * for LED based backlights using the CIE1931 algorithm. + */ +static +int pwm_backlight_brightness_default(struct device *dev, + struct platform_pwm_backlight_data *data, + unsigned int period) +{ + unsigned int counter = 0; + unsigned int i, n; + u64 retval; + + /* + * Count the number of bits needed to represent the period number. The + * number of bits is used to calculate the number of levels used for the + * brightness-levels table, the purpose of this calculation is have a + * pre-computed table with enough levels to get linear brightness + * perception. The period is divided by the number of bits so for a + * 8-bit PWM we have 255 / 8 = 32 brightness levels or for a 16-bit PWM + * we have 65535 / 16 = 4096 brightness levels. + * + * Note that this method is based on empirical testing on different + * devices with PWM of 8 and 16 bits of resolution. + */ + n = period; + while (n) { + counter += n % 2; + n >>= 1; + } + + data->max_brightness = DIV_ROUND_UP(period, counter); + data->levels = devm_kcalloc(dev, data->max_brightness, + sizeof(*data->levels), GFP_KERNEL); + if (!data->levels) + return -ENOMEM; + + /* Fill the table using the cie1931 algorithm */ + for (i = 0; i < data->max_brightness; i++) { + retval = cie1931((i * PWM_LUMINANCE_SCALE) / + data->max_brightness, PWM_LUMINANCE_SCALE) * + period; + retval = DIV_ROUND_CLOSEST_ULL(retval, PWM_LUMINANCE_SCALE); + if (retval > UINT_MAX) + return -EINVAL; + data->levels[i] = (unsigned int)retval; + } + + data->dft_brightness = data->max_brightness / 2; + data->max_brightness--; + + return 0; +} + static int pwm_backlight_parse_dt(struct device *dev, struct platform_pwm_backlight_data *data) { struct device_node *node = dev->of_node; + unsigned int num_levels = 0; + unsigned int levels_count; + unsigned int num_steps = 0; struct property *prop; + unsigned int *table; int length; u32 value; int ret; @@ -157,16 +262,20 @@ static int pwm_backlight_parse_dt(struct device *dev, memset(data, 0, sizeof(*data)); - /* determine the number of brightness levels */ + /* + * Determine the number of brightness levels, if this property is not + * set a default table of brightness levels will be used. + */ prop = of_find_property(node, "brightness-levels", &length); if (!prop) - return -EINVAL; + return 0; data->max_brightness = length / sizeof(u32); /* read brightness levels from DT property */ if (data->max_brightness > 0) { size_t size = sizeof(*data->levels) * data->max_brightness; + unsigned int i, j, n = 0; data->levels = devm_kzalloc(dev, size, GFP_KERNEL); if (!data->levels) @@ -184,6 +293,84 @@ static int pwm_backlight_parse_dt(struct device *dev, return ret; data->dft_brightness = value; + + /* + * This property is optional, if is set enables linear + * interpolation between each of the values of brightness levels + * and creates a new pre-computed table. + */ + of_property_read_u32(node, "num-interpolated-steps", + &num_steps); + + /* + * Make sure that there is at least two entries in the + * brightness-levels table, otherwise we can't interpolate + * between two points. + */ + if (num_steps) { + if (data->max_brightness < 2) { + dev_err(dev, "can't interpolate\n"); + return -EINVAL; + } + + /* + * Recalculate the number of brightness levels, now + * taking in consideration the number of interpolated + * steps between two levels. + */ + for (i = 0; i < data->max_brightness - 1; i++) { + if ((data->levels[i + 1] - data->levels[i]) / + num_steps) + num_levels += num_steps; + else + num_levels++; + } + num_levels++; + dev_dbg(dev, "new number of brightness levels: %d\n", + num_levels); + + /* + * Create a new table of brightness levels with all the + * interpolated steps. + */ + size = sizeof(*table) * num_levels; + table = devm_kzalloc(dev, size, GFP_KERNEL); + if (!table) + return -ENOMEM; + + /* Fill the interpolated table. */ + levels_count = 0; + for (i = 0; i < data->max_brightness - 1; i++) { + value = data->levels[i]; + n = (data->levels[i + 1] - value) / num_steps; + if (n > 0) { + for (j = 0; j < num_steps; j++) { + table[levels_count] = value; + value += n; + levels_count++; + } + } else { + table[levels_count] = data->levels[i]; + levels_count++; + } + } + table[levels_count] = data->levels[i]; + + /* + * As we use interpolation lets remove current + * brightness levels table and replace for the + * new interpolated table. + */ + devm_kfree(dev, data->levels); + data->levels = table; + + /* + * Reassign max_brightness value to the new total number + * of brightness levels. + */ + data->max_brightness = num_levels; + } + data->max_brightness--; } @@ -211,6 +398,14 @@ static int pwm_backlight_parse_dt(struct device *dev, { return -ENODEV; } + +static +int pwm_backlight_brightness_default(struct device *dev, + struct platform_pwm_backlight_data *data, + unsigned int period) +{ + return -ENODEV; +} #endif static int pwm_backlight_initial_power_state(const struct pwm_bl_data *pb) @@ -251,7 +446,9 @@ static int pwm_backlight_probe(struct platform_device *pdev) struct backlight_device *bl; struct device_node *node = pdev->dev.of_node; struct pwm_bl_data *pb; + struct pwm_state state; struct pwm_args pargs; + unsigned int i; int ret; if (!data) { @@ -276,17 +473,6 @@ static int pwm_backlight_probe(struct platform_device *pdev) goto err_alloc; } - if (data->levels) { - unsigned int i; - - for (i = 0; i <= data->max_brightness; i++) - if (data->levels[i] > pb->scale) - pb->scale = data->levels[i]; - - pb->levels = data->levels; - } else - pb->scale = data->max_brightness; - pb->notify = data->notify; pb->notify_after = data->notify_after; pb->check_fb = data->check_fb; @@ -353,6 +539,26 @@ static int pwm_backlight_probe(struct platform_device *pdev) dev_dbg(&pdev->dev, "got pwm for backlight\n"); + if (!data->levels) { + /* Get the PWM period (in nanoseconds) */ + pwm_get_state(pb->pwm, &state); + + ret = pwm_backlight_brightness_default(&pdev->dev, data, + state.period); + if (ret < 0) { + dev_err(&pdev->dev, + "failed to setup default brightness table\n"); + goto err_alloc; + } + } + + for (i = 0; i <= data->max_brightness; i++) { + if (data->levels[i] > pb->scale) + pb->scale = data->levels[i]; + + pb->levels = data->levels; + } + /* * FIXME: pwm_apply_args() should be removed when switching to * the atomic PWM API. diff --git a/include/linux/backlight.h b/include/linux/backlight.h index 7fbf0539e14a..0b5897446dca 100644 --- a/include/linux/backlight.h +++ b/include/linux/backlight.h @@ -79,7 +79,6 @@ struct backlight_properties { /* Backlight type */ enum backlight_type type; /* Flags used to signal drivers of state changes */ - /* Upper 4 bits are reserved for driver internal use */ unsigned int state; #define BL_CORE_SUSPENDED (1 << 0) /* backlight is suspended */ |